Prime Minister David Cameron delivers a speech on EU renegotiation, at Chatham House in London.

The person who could exert most influence over voters in the upcoming European Union referendum is not a politician, businessman or celebrity. It is Martin Lewis, the Money Saving Expert.

According to a new survey conducted by Ed Miliband's former pollster, James Morris, the referendum is on a "knife edge", with the 'Remain' campaign ahead by just three-points.

Writing on The Huffington Post today, Morris, says the results of the Greenberg Quinlan Rosner poll show Lewis is trusted by 71% of people when he makes arguments about Europe - despite not having made notable interventions into the debate.

He is thirteen points ahead of the next most trust person on the Europe question: inventor James Dyson.

Stuart Rose, the chairman of the pro-EU 'Britain Stronger In Europe' campaign, is trusted by just 36%. John Major and Gordon Brown score just below 50%. But Tony Blair is trusted by just 32%.

In his blog, Morris also says it will be crucial for David Cameron to keep the Conservative Party as united as possible behind 'Remain'.

"If David Cameron succeeds in his efforts to negotiate a better deal from the EU, our new poll shows that he adds 10 points to the power of the remain campaign's argument with swing voters. But that is far from the biggest prize when it comes to winning the referendum." he says.

"His real goal is political management - to soothe internal Tory party angst such that he can safely be on the remain side, and none of his potential successors front up for 'Leave'.

"The Tory vote currently breaks 50 to 43 in favour of leaving. However, the pattern in second order elections like referenda is that partisan voters end up voting with their party. With 85% of Tories trusting David Cameron and 81% saying they trust Boris Johnson, if those two shift to be firmly in favour of remaining in the EU, the Tory vote will follow, transforming the race.

"On the other hand, if the Tory party is seen as ambivalent and divided, voters won't get a clear cue from their party and the potential game changer is missed. With Tory party members strongly anti-EU, the real goal of this negotiation is to allow David Cameron to get decisively into the remain camp without losing his grip on his own party membership."

On Tuesday morning, the Cameron set out his main proposals to change the way the EU works ahead of a British referendum on our membership.

Cameron said the UK must be exempted from the commitment to "ever-closer union", be allowed to restrict benefits for migrants, get protection from eurozone integration, and see improvements in competitiveness.

But eurosceptic Tory MPs savaged the plan as "a pig in a poke", "purely symbolic" and "pretty thin gruel".